Lift truck safety control

ABSTRACT

An industrial lift truck with a power operated lift carriage has pivoted forks in a normal horizontal position to carry a load. Switches or valves in the carriage power control sense the position of the forks and prevent carriage movement when the forks are tilted from the normal position.

1Jnited States Patent Anderson et a1.

[ 1 May 30, 1972 LEFT TRUCK SAFETY CONTROL Richard N. Anderson; James W. Uetrecht, both of New Bremen, Ohio Inventors:

Assignee: Crown Controls Corporation, New

Bremen, Ohio June 29, 1970 Filed:

Appl. No.:

US. Cl ...187/9,187/34, 214/128 Int. Cl. ..B66b 5/02, B66b 9/20 Field of Search 1 87/9, 34; 214/15, 660, 730,

References Cited UNITED STATES PATENTS 4/1969 Nutter ..187/9 Mosel ..187/9 X Calabrese... ...214/15 R Turner 187/9 X Quayle ...2l4/730 May ..2l4/660 X Primary ExaminerEvon C. Blunk Assistant Examiner-W. Scott Carson An0rneyMarecha1, Biebel, French & Bug

ABSTRACT An industrial lift truck with a power operated lift carriage has pivoted forks in a normal horizontal position to carry a load. Switches or valves in the carriage power control sense the position of the forks and prevent carriage movement when the forks are tilted from the normal position.

6 Claims, 5 Drawing Figures Patented May 30, 1972 FIG-1 FIG -2 FIG -4 IN VE/V TORS w wm RC E R T AE NU D W s HE m RJ ATTOR/VE Y5 LIFT TRUCK SAFETY CONTROL BACKGROUND OF THE INVENTION This invention relates to an improvement in industrial lift trucks. A typical lift truck has a supporting frame with ground engaging wheels, and a mast structure extending vertically from the frame and supporting the power lift mechanism. The frame is usually supported on wheels, and may be either propelled manually or self-propelled.

In operation, the load or material to be moved, usually on a Pallet, is engaged by the lift mechanism which typically has forks extending outwardly from the carriage to engage the underside of the material. The material may be lifted by the forks and carried to the desired location. The material may be lowered or stacked on other items or racks, and the forks are then disengaged. If the operator is hurried, careless, or distracted, the forks may not be entirely withdrawn from the pallet and/or material, particularly when the load is stacked on other items or racks before the lowering of the forks is begun. As a result, the fork, being lowered as it is withdrawing, catches on the other items or racks, tipping the forks upward and either moves the material from its desired position, or dumps it altogether. In addition to damage to the material and surroundings, the operator or other nearby personnel may be harmed. This is particularly so in the case of so-called stock picker trucks on which the operator rides a platform on the lift carriage. This may occur especially in areas allowing minimum movement where the operator of the truck cannot always ascertain if the forks are completely clear.

SUMMARY OF THE INVENTION The tines or forks of the lift mechanism, according to the present invention, are partially rotatable about a horizontal axis. That is, the end of each fork farthest from the lift carriage can move from its normally horizontal position upwards through a substantial arc, perhaps as much as 70 to 90". When in the normal position, the end of each fork closest to the carriage is in contact with a stop on the bottom of the carriage. A sensor, such as a switch or valve, is mounted near the stop, preferably on the carriage, to sense the position of the forks in relation to the carriage. If, after the operator has unloaded material and begins to lower the carriage before the forks are clear of the supporting items, this will result in rotation of one of both forks, one or both of the sensors will sense that the end(s) of the forks closest the carriage are not in contact with the-stops and causes the carriage to cease movement. As a result, the operator will be able to correct the position of the truck allowing proper withdrawal without danger of moving or dumping the material being handled. The sensors function automatically if the carriage is lowered prematurely.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a lift truck incorporating the invention;

FIG. 2 is an enlarged view of the forks;

FIG. 3 is a schematic diagram of the hydraulic system and sensor circuit;

FIG. 4 is a diagram of a modified sensor control circuit; and

FIG. 5 is a view of another form of fork assembly and associated sensors.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 and FIG. 2, which show a preferred embodiment of the invention, a stock picker truck has a mast section 12 and a carriage part 14. The carriage is vertically movable on mast 12, as later described. Tines or forks are pivotably attached to carriage 14 at pivot points 16, which are forward of the carriage on supporting arms 17. Switches 18 are mounted at the base of the carriage 14 for contact with forks 15 when the fork is in its normal horizontal position, against the underside of the arms which functions as a stop means for each fork. However, when carriage 14 is lowered and either fork 15 strikes an obstruction 19, something beneath the material just off-loaded, the fork moves about pivot point 16 to a position 15. This movement actuates the corresponding switch 18 which in turn causes carriage 14 to cease movement, as later described. The operator rides a platform 20 adjacent the carriage, and the usual controls (not designated) are located at this position. 7

FIG. 3 depicts, schematically, thepower system employed to operate the lift carriage, together with the switches 18. Hydraulic cylinder 22 includes a piston which is connected to the carriage 14 in a conventional way. The hydraulic cylinder is connected to the output of a pump 23 through a check valve 24. The pump takes fluid from a supply tank 25 and is driven by an electric motor 27 controlled by a raise or lift switch 28 to lift the carriage and any load carried on the forks. The carriage lowers by gravity. A solenoid operated dump valve 30 is connected in a line 31 extending from cylinder 22 to tank 25, and normally blocking flow through this line. A manually operated lowering switch 32 is connected in a circuit for electrical power to the solenoid, for shifting valve 30 to its open position.

The switches 18 are depicted schematically in FIG. 3 and are normally closed in use, but are spring urged toward an open position. Each switch 18 will open whenever the corresponding fork 15 moves from its normal or stop position, to break the circuit and deenergize solenoid valve 30, which will interrupt the flow of hydraulic fluid in line 31. The result is that carriage 14 will stop in whatever position it happens to be, and will not move until the fork, now in a somewhat tilted position, returns to its normal or horizontal position.

Thus, when one or both forks come in contact with an obstruction during lowering of the carriage, the switches 18 will function as sensors causing the fork and carriage to cease movement until the operator can correct the condition by raising the forks and can maneuver the lift truck clear of the obstruction, at which time the fork will drop to its normal position and lowering of the carriage can continue.

In some lift trucks, for example those used in hazardous areas, electrical circuits may not be employed. In such instances, as well as in other cases where it may be more convenient from the standpoint of simplicity, the same safety arrangement can be provided using hydraulic valve control sensors. In FIG. 4, a valve 30a is shown controlling flow through the dump line 31a, corresponding to similar parts in FIG. 3. Connected in series in this line are spring loaded valves 35 which normally are held in the position shown by pusher members 36 responsive to the normal position of the forks. Thus, if

' the forks are in the normal horizontal position, flow through dump line 31a occurs whenever valve 30a is open. If either fork is tilted from the normal position, the force from the pusher member 46 will be removed and the spring will shift the appropriate valve 35 to block flow through the dump line 31a until the fork returns to its normal position.

FIG. 5 shows application of the invention to another commonly used fork configuration and mounting. Here, a mast 12b supports a carriage 14b with generally L-shaped forks 15b being connected to the carriage through pivots 16b. The forks extend downward from the pivot connection and then outward from the carriage. The sensors, which may be of either the electrical switch or valve type as described above, are indicated at 18b, extending generally horizontally to sense motion of the corner of the fork 15b away from the carriage, indicating an upward tilting of the fork. As in the previous arrangements, this will result in appropriate blocking of the dump circuit from the lift cylinder, preventing further lowering of the carriage until the fork returns to its normal position.

While the forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. In a lift truck mechanism including a vertically movable carriage having power operated means for controlling the raising and lowering of said carriage, spaced arms attached to and extending outwardly from said carriage and each having a pivot connection thereon, a load supporting fork pivotally attached to each of said pivot connections and projecting outwardly from said arms, and stop means defining the normal operating position of each of said forks relative to said arms; the improvement comprising, sensor means operable in response to movement of said forks about said pivots and away from said normal operating position resulting from the lowering of said carriage, said sensors being connected to said power operated means to inhibit further lowering of said carriage until said forks are returned to their normal operating position.

2. The apparatus defined in claim 1 wherein said power operated means comprises an hydraulic system including a pump, a fluid supply tank to supply fluid to said pump, an hydraulic cylinder actuated by fluid from said pump and connected to move said carriage, a valve between said pump and said cylinder, and a control circuit for said valve controlled by said sensor means to stop said cylinder in response to actuation of said sensor means by movement of a fork from its normal position.

3. In an automatic safety control for the lift mechanism of a mobile lift truck, having a mast, a power driven lift carriage on said mast, and forks pivoted on said carriage and normally in a horizontal load carrying position; the improvement comprising sensor means actuatable in response to movement relative to said carriage of any one of said forks from said normal position, and a control circuit operative by actuation of said sensor means to halt lowering said lift carriage until said forks resume their normal position.

4. A safety control for a lift truck as defined in claim 3, wherein said control circuit includes a solenoid operated valve connected to control downward motion of said carriage, and wherein said sensor means are electrical sensor switches, said control circuit having a lowering control switch of actuation for said solenoid operated valve, and said lowering control switch and said sensor switches all being in a series connection requiring completion of the circuit through each of such switches to lower the carriage.

5. A safety control for a lift truck as defined in claim 3, wherein said control circuit includes a lowering control valve and said sensor means are valve operating members, a sensor valve responsive to each of said valve operating members, and said control valve and said sensor valves being connected in series relation requiring flow through all of such valves to lower the carriage.

6. In a lift truck mechanism including a vertically movable carriage having power operated means for controlling the raising and lowering of said carriage, spaced arms attached to and extending outwardly from said carriage and each having a pivot connection thereon, a load supporting fork pivotally attached to each of said pivot connections and projecting outwardly from said arms, and stop means defining the normal operating position of each of said forks relative to said arms; the improvement comprising, sensor means operable in response to movement of said forks about said pivots and away from said normal operating position and connected to said power operated means to inhibit further movement of said carriage in a direction causing further movement of said forks away from said normal operating position, said sensor means inhibiting said further carriage movement until said forks are returned to their normal operating position. 

1. In a lift truck mechanism including a vertically movable carriage having power operated means for controlling the raising and lowering of said carriage, spaced arms attached to and extending outwardly from said carriage and each having a pivot connection thereon, a load supporting fork pivotally attached to each of said pivot connections and projecting outwardly from said arms, and stop means defining the normal operating position of each of said forks relative to said arms; the improvement comprising, sensor means operable in response to movement of said forks about said pivots and away from said normal operating position resulting from the lowering of said carriage, said sensors being connected to said power operated means to inhibit further lowering of said carriage until said forks are returned to their normal operating position.
 2. The apparatus defined in claim 1 wherein said power operated means comprises an hydraulic system including a pump, a fluid supply tank to supply fluid to said pump, an hydraulic cylinder actuated by fluid from said pump and connected to move said carriage, a valve between said pump and said cylinder, and a control circuit for said valve controlled by said sensor means to stop said cylinder in response to actuation of said sensor means by movement of a fork from its normal position.
 3. In an automatic safety control for the lift mechanism of a mobile lift truck, having a mast, a power driven lift carriage on said mast, and forks pivoted on said carriage and normally in a horizontal load carrying position; the improvement comprising sensor means actuatable in response to movement relative to said carriage of any one of said forks from said normal position, and a control circuit operative by actuation of said sensor means to halt lowering said lift carriage until said forks resume their normal position.
 4. A safety control for a lift truck as defined in claim 3, wherein said control circuit includes a solenoid operated valve connected to control downward motion of said carriage, and wherein said sensor means are electrical sensor switches, said control circuit having a lowering control switch of actuation for said solenoid operated valve, and said lowering control switch and said sensor switches all being in a series connection requiring completion of the circuit through each of such switches to lower the carriage.
 5. A safety control for a lift truck as defined in claim 3, wherein said control circuit includes a lowering control valve and said sensor means are valve operating members, a sensor valve responsive to each of said valve operating members, and said control valve and said sensor valves being connected in series relation requiring flow through all of such valves to lower the carriage.
 6. In a lift truck mechanism including a vertically movable carriage having power operated means for controlling the raising and lowering of said carriage, spaced arms attached to and extending outwardly from said carriage and each having a pivot connection thereon, a load supporting fork pivotally attached to each of said pivot connections and projecting outwardly from said arms, and stop means defining the normal operating position of each of said forks relative to said arms; the improvement comprising, sensor means operable in response to movement of said forks about said pivots and away from said normal operating position and connected to said power operated means to inhibit further movement of said carriage in a direction causing further movement of said forks away from said normal operating position, said sensor means inhibiting said further carriage movement until said forks are returned to their normal operating position. 